The present invention relates to a cutting device for cutting straw and similar material into pieces, of the type which comprises a driven shaft kept in a housing, where said shaft is provided with longitudinally proceeding rows of knife attachments for knives, which extends radially from the shaft and are provided with cutting edges, whereby said knives under operation pass between a row of counter knives directed towards said shaft and in the same way suitably are provided with cutting edges, whereby the straw material to be cut is being fed towards said counter arms.
Cutting devices for the cutting of straw and the like into pieces are previously known, which comprises a rotating drum shaft, on which pivotable knives are arranged in rows, which knives through their passage between counter knives cut fed straw material, compare for instance GB-A-1,060,179. These known devices have always exhibited as a maximum, four rows of knives, usually arranged in pairs opposite each other or with the rows slightly displaced in respect to adjacent rows. The problem with the known devices is a limited amount of cutting, the average cutting length being too long and too low a level of splintering, which severely affects the ability of mouldering of the cut straw, even if the knife rotor normally works with a high rotational speed, which requires a high energy input.
A cutting device for cutting turnip tops and other green fodder to be ensilaged is previously known from SE 117 423 C, where a high degree of decomposition is required, which one has attempted to achieve by means of the arrangement of six rows of knives. As long as the green fodder is fresh, even a four-row cutting device will manage the required degree of cutting, but not when the material is dry and tough. The device must also tolerate that stones can be brought with the green fodder into the cutting device. This problem has been solved, by the removal of the traditional, rigid counter knives and instead transporting the green fodder to, in the rotational direction of the knife rotor, the rear half of the drum, where an opening is arranged through which the stones may leave the device.
Since the known cutting device lacks counter knives, it can not be used for cutting straw or the like, additionally would it, due to its particular construction, very rapidly become jammed by uncut straw as the material to be cut has to be fed more than 180xc2x0 through the housing.
The purpose of the present invention is to provide a cutting device, which:
has a large input opening for straw,
has a higher cutting capacity per time period,
gives a shorter average cut length than conventional devices,
has a high splinter degree,
has a high peripherical speed,
has a smoother operation,
has a lower noise level,
and this at essentially the same energy demand as a conventional cutting device.
Surprisingly, it has now been shown possible to increase the cutting capacity with a device according to the invention, which has at least six rows of knives distributed over the periphery of the shaft drum and which extend over essentially the whole width of the threshing machine, which provides for the increase of the straw input opening. The increased number of knife rows and the fact that each knife attachment carries double, pivotable knives has lead to a major increase of the capacity.
The greater number of pivotable knives has also lead to the corresponding increase of the number of rigid counter knives, leading to a decreased average cutting length and a higher degree of splintering of the straw, at the same time as increasing the peripherical speed at the same rotation speed, by increasing the diameter of the shaft drum of the knives.
A smoother operation and a better balancing, and a lower noise level have been reached experimentally, by placing the knife attachments to the shaft drum in such way that they follow a sinusoidal helicoidal line.